Sentarō
Kotsubaki

Sentarō Kotsubaki shared the 3rd Seat of the 13th Division with Kiyone Kotetsu, an arrangement that exists mainly so the two of them can compete over which one is more devoted to Jūshirō Ukitake. They shout over each other constantly, race to deliver reports, and interpret any instruction as a contest.

Ukitake's illness is why the arrangement matters. A captain who spends long stretches unable to leave his estate needs officers who will run the division without being asked, and the pair of them do it while behaving like children about the credit. Sentarō is the loud one, and Kiyone's main objection to him is the volume.

When the Sōkyoku begins its release on the morning of Rukia Kuchiki's execution, he is the one who spots it and yells for the captain, and Kiyone tells him off for yelling while doing exactly the same thing. After Ukitake's death and the reorganisation that follows, Sentarō becomes lieutenant of the 13th Division under Rukia, the officer they used to fetch tea for. The comedy pairing turns out to have been two competent people the whole time.